2 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
3 * The Regents of the University of California. All rights reserved.
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
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12 * documentation and/or other materials provided with the distribution.
13 * 3. Neither the name of the University nor the names of its contributors
14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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29 * @(#)tcp_output.c 8.4 (Berkeley) 5/24/95
32 #include <sys/cdefs.h>
33 __FBSDID("$FreeBSD$");
36 #include "opt_inet6.h"
37 #include "opt_ipsec.h"
38 #include "opt_tcpdebug.h"
40 #include <sys/param.h>
41 #include <sys/systm.h>
42 #include <sys/domain.h>
44 #include <sys/hhook.h>
46 #include <sys/kernel.h>
49 #include <sys/mutex.h>
50 #include <sys/protosw.h>
52 #include <sys/socket.h>
53 #include <sys/socketvar.h>
54 #include <sys/sysctl.h>
57 #include <net/route.h>
60 #include <netinet/in.h>
61 #include <netinet/in_kdtrace.h>
62 #include <netinet/in_systm.h>
63 #include <netinet/ip.h>
64 #include <netinet/in_pcb.h>
65 #include <netinet/ip_var.h>
66 #include <netinet/ip_options.h>
68 #include <netinet6/in6_pcb.h>
69 #include <netinet/ip6.h>
70 #include <netinet6/ip6_var.h>
73 #include <netinet/tcp_fastopen.h>
75 #include <netinet/tcp.h>
77 #include <netinet/tcp_fsm.h>
78 #include <netinet/tcp_seq.h>
79 #include <netinet/tcp_timer.h>
80 #include <netinet/tcp_var.h>
81 #include <netinet/tcpip.h>
82 #include <netinet/cc/cc.h>
84 #include <netinet/tcp_pcap.h>
87 #include <netinet/tcp_debug.h>
90 #include <netinet/tcp_offload.h>
93 #include <netipsec/ipsec_support.h>
95 #include <machine/in_cksum.h>
97 #include <security/mac/mac_framework.h>
99 VNET_DEFINE(int, path_mtu_discovery) = 1;
100 SYSCTL_INT(_net_inet_tcp, OID_AUTO, path_mtu_discovery, CTLFLAG_VNET | CTLFLAG_RW,
101 &VNET_NAME(path_mtu_discovery), 1,
102 "Enable Path MTU Discovery");
104 VNET_DEFINE(int, tcp_do_tso) = 1;
105 #define V_tcp_do_tso VNET(tcp_do_tso)
106 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_VNET | CTLFLAG_RW,
107 &VNET_NAME(tcp_do_tso), 0,
108 "Enable TCP Segmentation Offload");
110 VNET_DEFINE(int, tcp_sendspace) = 1024*32;
111 #define V_tcp_sendspace VNET(tcp_sendspace)
112 SYSCTL_INT(_net_inet_tcp, TCPCTL_SENDSPACE, sendspace, CTLFLAG_VNET | CTLFLAG_RW,
113 &VNET_NAME(tcp_sendspace), 0, "Initial send socket buffer size");
115 VNET_DEFINE(int, tcp_do_autosndbuf) = 1;
116 #define V_tcp_do_autosndbuf VNET(tcp_do_autosndbuf)
117 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_auto, CTLFLAG_VNET | CTLFLAG_RW,
118 &VNET_NAME(tcp_do_autosndbuf), 0,
119 "Enable automatic send buffer sizing");
121 VNET_DEFINE(int, tcp_autosndbuf_inc) = 8*1024;
122 #define V_tcp_autosndbuf_inc VNET(tcp_autosndbuf_inc)
123 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_inc, CTLFLAG_VNET | CTLFLAG_RW,
124 &VNET_NAME(tcp_autosndbuf_inc), 0,
125 "Incrementor step size of automatic send buffer");
127 VNET_DEFINE(int, tcp_autosndbuf_max) = 2*1024*1024;
128 #define V_tcp_autosndbuf_max VNET(tcp_autosndbuf_max)
129 SYSCTL_INT(_net_inet_tcp, OID_AUTO, sendbuf_max, CTLFLAG_VNET | CTLFLAG_RW,
130 &VNET_NAME(tcp_autosndbuf_max), 0,
131 "Max size of automatic send buffer");
134 * Make sure that either retransmit or persist timer is set for SYN, FIN and
137 #define TCP_XMIT_TIMER_ASSERT(tp, len, th_flags) \
138 KASSERT(((len) == 0 && ((th_flags) & (TH_SYN | TH_FIN)) == 0) ||\
139 tcp_timer_active((tp), TT_REXMT) || \
140 tcp_timer_active((tp), TT_PERSIST), \
141 ("neither rexmt nor persist timer is set"))
144 static void inline hhook_run_tcp_est_out(struct tcpcb *tp,
145 struct tcphdr *th, struct tcpopt *to,
146 uint32_t len, int tso);
148 static void inline cc_after_idle(struct tcpcb *tp);
152 * Wrapper for the TCP established output helper hook.
155 hhook_run_tcp_est_out(struct tcpcb *tp, struct tcphdr *th,
156 struct tcpopt *to, uint32_t len, int tso)
158 struct tcp_hhook_data hhook_data;
160 if (V_tcp_hhh[HHOOK_TCP_EST_OUT]->hhh_nhooks > 0) {
164 hhook_data.len = len;
165 hhook_data.tso = tso;
167 hhook_run_hooks(V_tcp_hhh[HHOOK_TCP_EST_OUT], &hhook_data,
174 * CC wrapper hook functions
177 cc_after_idle(struct tcpcb *tp)
179 INP_WLOCK_ASSERT(tp->t_inpcb);
181 if (CC_ALGO(tp)->after_idle != NULL)
182 CC_ALGO(tp)->after_idle(tp->ccv);
186 * Tcp output routine: figure out what should be sent and send it.
189 tcp_output(struct tcpcb *tp)
191 struct socket *so = tp->t_inpcb->inp_socket;
193 uint32_t recwin, sendwin;
194 int off, flags, error = 0; /* Keep compiler happy */
196 struct ip *ip = NULL;
197 struct ipovly *ipov = NULL;
199 u_char opt[TCP_MAXOLEN];
200 unsigned ipoptlen, optlen, hdrlen;
201 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
202 unsigned ipsec_optlen = 0;
205 int sack_rxmit, sack_bytes_rxmt;
210 int maxburst = TCP_MAXBURST;
213 struct ip6_hdr *ip6 = NULL;
216 isipv6 = (tp->t_inpcb->inp_vflag & INP_IPV6) != 0;
219 INP_WLOCK_ASSERT(tp->t_inpcb);
222 if (tp->t_flags & TF_TOE)
223 return (tcp_offload_output(tp));
228 * For TFO connections in SYN_RECEIVED, only allow the initial
229 * SYN|ACK and those sent by the retransmit timer.
231 if (IS_FASTOPEN(tp->t_flags) &&
232 (tp->t_state == TCPS_SYN_RECEIVED) &&
233 SEQ_GT(tp->snd_max, tp->snd_una) && /* initial SYN|ACK sent */
234 (tp->snd_nxt != tp->snd_una)) /* not a retransmit */
238 * Determine length of data that should be transmitted,
239 * and flags that will be used.
240 * If there is some data or critical controls (SYN, RST)
241 * to send, then transmit; otherwise, investigate further.
243 idle = (tp->t_flags & TF_LASTIDLE) || (tp->snd_max == tp->snd_una);
244 if (idle && ticks - tp->t_rcvtime >= tp->t_rxtcur)
246 tp->t_flags &= ~TF_LASTIDLE;
248 if (tp->t_flags & TF_MORETOCOME) {
249 tp->t_flags |= TF_LASTIDLE;
255 * If we've recently taken a timeout, snd_max will be greater than
256 * snd_nxt. There may be SACK information that allows us to avoid
257 * resending already delivered data. Adjust snd_nxt accordingly.
259 if ((tp->t_flags & TF_SACK_PERMIT) &&
260 SEQ_LT(tp->snd_nxt, tp->snd_max))
265 off = tp->snd_nxt - tp->snd_una;
266 sendwin = min(tp->snd_wnd, tp->snd_cwnd);
268 flags = tcp_outflags[tp->t_state];
270 * Send any SACK-generated retransmissions. If we're explicitly trying
271 * to send out new data (when sendalot is 1), bypass this function.
272 * If we retransmit in fast recovery mode, decrement snd_cwnd, since
273 * we're replacing a (future) new transmission with a retransmission
274 * now, and we previously incremented snd_cwnd in tcp_input().
277 * Still in sack recovery , reset rxmit flag to zero.
283 if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags) &&
284 (p = tcp_sack_output(tp, &sack_bytes_rxmt))) {
288 imax(min(tp->snd_wnd, tp->snd_cwnd) - sack_bytes_rxmt, 0);
289 /* Do not retransmit SACK segments beyond snd_recover */
290 if (SEQ_GT(p->end, tp->snd_recover)) {
292 * (At least) part of sack hole extends beyond
293 * snd_recover. Check to see if we can rexmit data
296 if (SEQ_GEQ(p->rxmit, tp->snd_recover)) {
298 * Can't rexmit any more data for this hole.
299 * That data will be rexmitted in the next
300 * sack recovery episode, when snd_recover
301 * moves past p->rxmit.
304 goto after_sack_rexmit;
306 /* Can rexmit part of the current hole */
307 len = ((int32_t)ulmin(cwin,
308 tp->snd_recover - p->rxmit));
310 len = ((int32_t)ulmin(cwin, p->end - p->rxmit));
311 off = p->rxmit - tp->snd_una;
312 KASSERT(off >= 0,("%s: sack block to the left of una : %d",
317 TCPSTAT_INC(tcps_sack_rexmits);
318 TCPSTAT_ADD(tcps_sack_rexmit_bytes,
319 min(len, tp->t_maxseg));
324 * Get standard flags, and add SYN or FIN if requested by 'hidden'
327 if (tp->t_flags & TF_NEEDFIN)
329 if (tp->t_flags & TF_NEEDSYN)
332 SOCKBUF_LOCK(&so->so_snd);
334 * If in persist timeout with window of 0, send 1 byte.
335 * Otherwise, if window is small but nonzero
336 * and timer expired, we will send what we can
337 * and go to transmit state.
339 if (tp->t_flags & TF_FORCEDATA) {
342 * If we still have some data to send, then
343 * clear the FIN bit. Usually this would
344 * happen below when it realizes that we
345 * aren't sending all the data. However,
346 * if we have exactly 1 byte of unsent data,
347 * then it won't clear the FIN bit below,
348 * and if we are in persist state, we wind
349 * up sending the packet without recording
350 * that we sent the FIN bit.
352 * We can't just blindly clear the FIN bit,
353 * because if we don't have any more data
354 * to send then the probe will be the FIN
357 if (off < sbused(&so->so_snd))
361 tcp_timer_activate(tp, TT_PERSIST, 0);
367 * If snd_nxt == snd_max and we have transmitted a FIN, the
368 * offset will be > 0 even if so_snd.sb_cc is 0, resulting in
369 * a negative length. This can also occur when TCP opens up
370 * its congestion window while receiving additional duplicate
371 * acks after fast-retransmit because TCP will reset snd_nxt
372 * to snd_max after the fast-retransmit.
374 * In the normal retransmit-FIN-only case, however, snd_nxt will
375 * be set to snd_una, the offset will be 0, and the length may
378 * If sack_rxmit is true we are retransmitting from the scoreboard
379 * in which case len is already set.
381 if (sack_rxmit == 0) {
382 if (sack_bytes_rxmt == 0)
383 len = ((int32_t)ulmin(sbavail(&so->so_snd), sendwin) -
389 * We are inside of a SACK recovery episode and are
390 * sending new data, having retransmitted all the
391 * data possible in the scoreboard.
393 len = ((int32_t)min(sbavail(&so->so_snd), tp->snd_wnd) -
396 * Don't remove this (len > 0) check !
397 * We explicitly check for len > 0 here (although it
398 * isn't really necessary), to work around a gcc
399 * optimization issue - to force gcc to compute
400 * len above. Without this check, the computation
401 * of len is bungled by the optimizer.
404 cwin = tp->snd_cwnd -
405 (tp->snd_nxt - tp->sack_newdata) -
409 len = imin(len, cwin);
415 * Lop off SYN bit if it has already been sent. However, if this
416 * is SYN-SENT state and if segment contains data and if we don't
417 * know that foreign host supports TAO, suppress sending segment.
419 if ((flags & TH_SYN) && SEQ_GT(tp->snd_nxt, tp->snd_una)) {
420 if (tp->t_state != TCPS_SYN_RECEIVED)
424 * When sending additional segments following a TFO SYN|ACK,
425 * do not include the SYN bit.
427 if (IS_FASTOPEN(tp->t_flags) &&
428 (tp->t_state == TCPS_SYN_RECEIVED))
435 * Be careful not to send data and/or FIN on SYN segments.
436 * This measure is needed to prevent interoperability problems
437 * with not fully conformant TCP implementations.
439 if ((flags & TH_SYN) && (tp->t_flags & TF_NOOPT)) {
446 * When retransmitting SYN|ACK on a passively-created TFO socket,
447 * don't include data, as the presence of data may have caused the
448 * original SYN|ACK to have been dropped by a middlebox.
450 if (IS_FASTOPEN(tp->t_flags) &&
451 (((tp->t_state == TCPS_SYN_RECEIVED) && (tp->t_rxtshift > 0)) ||
457 * If FIN has been sent but not acked,
458 * but we haven't been called to retransmit,
459 * len will be < 0. Otherwise, window shrank
460 * after we sent into it. If window shrank to 0,
461 * cancel pending retransmit, pull snd_nxt back
462 * to (closed) window, and set the persist timer
463 * if it isn't already going. If the window didn't
464 * close completely, just wait for an ACK.
466 * We also do a general check here to ensure that
467 * we will set the persist timer when we have data
468 * to send, but a 0-byte window. This makes sure
469 * the persist timer is set even if the packet
470 * hits one of the "goto send" lines below.
473 if ((sendwin == 0) && (TCPS_HAVEESTABLISHED(tp->t_state)) &&
474 (off < (int) sbavail(&so->so_snd))) {
475 tcp_timer_activate(tp, TT_REXMT, 0);
477 tp->snd_nxt = tp->snd_una;
478 if (!tcp_timer_active(tp, TT_PERSIST))
483 /* len will be >= 0 after this point. */
484 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
487 * Automatic sizing of send socket buffer. Often the send buffer
488 * size is not optimally adjusted to the actual network conditions
489 * at hand (delay bandwidth product). Setting the buffer size too
490 * small limits throughput on links with high bandwidth and high
491 * delay (eg. trans-continental/oceanic links). Setting the
492 * buffer size too big consumes too much real kernel memory,
493 * especially with many connections on busy servers.
495 * The criteria to step up the send buffer one notch are:
496 * 1. receive window of remote host is larger than send buffer
497 * (with a fudge factor of 5/4th);
498 * 2. send buffer is filled to 7/8th with data (so we actually
499 * have data to make use of it);
500 * 3. send buffer fill has not hit maximal automatic size;
501 * 4. our send window (slow start and cogestion controlled) is
502 * larger than sent but unacknowledged data in send buffer.
504 * The remote host receive window scaling factor may limit the
505 * growing of the send buffer before it reaches its allowed
508 * It scales directly with slow start or congestion window
509 * and does at most one step per received ACK. This fast
510 * scaling has the drawback of growing the send buffer beyond
511 * what is strictly necessary to make full use of a given
512 * delay*bandwidth product. However testing has shown this not
513 * to be much of an problem. At worst we are trading wasting
514 * of available bandwidth (the non-use of it) for wasting some
515 * socket buffer memory.
517 * TODO: Shrink send buffer during idle periods together
518 * with congestion window. Requires another timer. Has to
519 * wait for upcoming tcp timer rewrite.
521 * XXXGL: should there be used sbused() or sbavail()?
523 if (V_tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
524 if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat &&
525 sbused(&so->so_snd) >= (so->so_snd.sb_hiwat / 8 * 7) &&
526 sbused(&so->so_snd) < V_tcp_autosndbuf_max &&
527 sendwin >= (sbused(&so->so_snd) -
528 (tp->snd_nxt - tp->snd_una))) {
529 if (!sbreserve_locked(&so->so_snd,
530 min(so->so_snd.sb_hiwat + V_tcp_autosndbuf_inc,
531 V_tcp_autosndbuf_max), so, curthread))
532 so->so_snd.sb_flags &= ~SB_AUTOSIZE;
537 * Decide if we can use TCP Segmentation Offloading (if supported by
540 * TSO may only be used if we are in a pure bulk sending state. The
541 * presence of TCP-MD5, SACK retransmits, SACK advertizements and
542 * IP options prevent using TSO. With TSO the TCP header is the same
543 * (except for the sequence number) for all generated packets. This
544 * makes it impossible to transmit any options which vary per generated
547 * IPv4 handling has a clear separation of ip options and ip header
548 * flags while IPv6 combines both in in6p_outputopts. ip6_optlen() does
549 * the right thing below to provide length of just ip options and thus
550 * checking for ipoptlen is enough to decide if ip options are present.
552 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
554 * Pre-calculate here as we save another lookup into the darknesses
555 * of IPsec that way and can actually decide if TSO is ok.
558 if (isipv6 && IPSEC_ENABLED(ipv6))
559 ipsec_optlen = IPSEC_HDRSIZE(ipv6, tp->t_inpcb);
565 if (IPSEC_ENABLED(ipv4))
566 ipsec_optlen = IPSEC_HDRSIZE(ipv4, tp->t_inpcb);
571 ipoptlen = ip6_optlen(tp->t_inpcb);
574 if (tp->t_inpcb->inp_options)
575 ipoptlen = tp->t_inpcb->inp_options->m_len -
576 offsetof(struct ipoption, ipopt_list);
579 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
580 ipoptlen += ipsec_optlen;
583 if ((tp->t_flags & TF_TSO) && V_tcp_do_tso && len > tp->t_maxseg &&
584 ((tp->t_flags & TF_SIGNATURE) == 0) &&
585 tp->rcv_numsacks == 0 && sack_rxmit == 0 &&
590 if (SEQ_LT(p->rxmit + len, tp->snd_una + sbused(&so->so_snd)))
593 if (SEQ_LT(tp->snd_nxt + len, tp->snd_una +
594 sbused(&so->so_snd)))
598 recwin = lmin(lmax(sbspace(&so->so_rcv), 0),
599 (long)TCP_MAXWIN << tp->rcv_scale);
602 * Sender silly window avoidance. We transmit under the following
603 * conditions when len is non-zero:
605 * - We have a full segment (or more with TSO)
606 * - This is the last buffer in a write()/send() and we are
607 * either idle or running NODELAY
608 * - we've timed out (e.g. persist timer)
609 * - we have more then 1/2 the maximum send window's worth of
610 * data (receiver may be limited the window size)
611 * - we need to retransmit
614 if (len >= tp->t_maxseg)
617 * NOTE! on localhost connections an 'ack' from the remote
618 * end may occur synchronously with the output and cause
619 * us to flush a buffer queued with moretocome. XXX
621 * note: the len + off check is almost certainly unnecessary.
623 if (!(tp->t_flags & TF_MORETOCOME) && /* normal case */
624 (idle || (tp->t_flags & TF_NODELAY)) &&
625 (uint32_t)len + (uint32_t)off >= sbavail(&so->so_snd) &&
626 (tp->t_flags & TF_NOPUSH) == 0) {
629 if (tp->t_flags & TF_FORCEDATA) /* typ. timeout case */
631 if (len >= tp->max_sndwnd / 2 && tp->max_sndwnd > 0)
633 if (SEQ_LT(tp->snd_nxt, tp->snd_max)) /* retransmit case */
640 * Sending of standalone window updates.
642 * Window updates are important when we close our window due to a
643 * full socket buffer and are opening it again after the application
644 * reads data from it. Once the window has opened again and the
645 * remote end starts to send again the ACK clock takes over and
646 * provides the most current window information.
648 * We must avoid the silly window syndrome whereas every read
649 * from the receive buffer, no matter how small, causes a window
650 * update to be sent. We also should avoid sending a flurry of
651 * window updates when the socket buffer had queued a lot of data
652 * and the application is doing small reads.
654 * Prevent a flurry of pointless window updates by only sending
655 * an update when we can increase the advertized window by more
656 * than 1/4th of the socket buffer capacity. When the buffer is
657 * getting full or is very small be more aggressive and send an
658 * update whenever we can increase by two mss sized segments.
659 * In all other situations the ACK's to new incoming data will
660 * carry further window increases.
662 * Don't send an independent window update if a delayed
663 * ACK is pending (it will get piggy-backed on it) or the
664 * remote side already has done a half-close and won't send
665 * more data. Skip this if the connection is in T/TCP
668 if (recwin > 0 && !(tp->t_flags & TF_NEEDSYN) &&
669 !(tp->t_flags & TF_DELACK) &&
670 !TCPS_HAVERCVDFIN(tp->t_state)) {
672 * "adv" is the amount we could increase the window,
673 * taking into account that we are limited by
674 * TCP_MAXWIN << tp->rcv_scale.
680 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt)) {
681 oldwin = (tp->rcv_adv - tp->rcv_nxt);
687 * If the new window size ends up being the same as or less
688 * than the old size when it is scaled, then don't force
691 if (oldwin >> tp->rcv_scale >= (adv + oldwin) >> tp->rcv_scale)
694 if (adv >= (int32_t)(2 * tp->t_maxseg) &&
695 (adv >= (int32_t)(so->so_rcv.sb_hiwat / 4) ||
696 recwin <= (so->so_rcv.sb_hiwat / 8) ||
697 so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg))
699 if (2 * adv >= (int32_t)so->so_rcv.sb_hiwat)
705 * Send if we owe the peer an ACK, RST, SYN, or urgent data. ACKNOW
706 * is also a catch-all for the retransmit timer timeout case.
708 if (tp->t_flags & TF_ACKNOW)
710 if ((flags & TH_RST) ||
711 ((flags & TH_SYN) && (tp->t_flags & TF_NEEDSYN) == 0))
713 if (SEQ_GT(tp->snd_up, tp->snd_una))
716 * If our state indicates that FIN should be sent
717 * and we have not yet done so, then we need to send.
719 if (flags & TH_FIN &&
720 ((tp->t_flags & TF_SENTFIN) == 0 || tp->snd_nxt == tp->snd_una))
723 * In SACK, it is possible for tcp_output to fail to send a segment
724 * after the retransmission timer has been turned off. Make sure
725 * that the retransmission timer is set.
727 if ((tp->t_flags & TF_SACK_PERMIT) &&
728 SEQ_GT(tp->snd_max, tp->snd_una) &&
729 !tcp_timer_active(tp, TT_REXMT) &&
730 !tcp_timer_active(tp, TT_PERSIST)) {
731 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
735 * TCP window updates are not reliable, rather a polling protocol
736 * using ``persist'' packets is used to insure receipt of window
737 * updates. The three ``states'' for the output side are:
738 * idle not doing retransmits or persists
739 * persisting to move a small or zero window
740 * (re)transmitting and thereby not persisting
742 * tcp_timer_active(tp, TT_PERSIST)
743 * is true when we are in persist state.
744 * (tp->t_flags & TF_FORCEDATA)
745 * is set when we are called to send a persist packet.
746 * tcp_timer_active(tp, TT_REXMT)
747 * is set when we are retransmitting
748 * The output side is idle when both timers are zero.
750 * If send window is too small, there is data to transmit, and no
751 * retransmit or persist is pending, then go to persist state.
752 * If nothing happens soon, send when timer expires:
753 * if window is nonzero, transmit what we can,
754 * otherwise force out a byte.
756 if (sbavail(&so->so_snd) && !tcp_timer_active(tp, TT_REXMT) &&
757 !tcp_timer_active(tp, TT_PERSIST)) {
763 * No reason to send a segment, just return.
766 SOCKBUF_UNLOCK(&so->so_snd);
770 SOCKBUF_LOCK_ASSERT(&so->so_snd);
772 if (len >= tp->t_maxseg)
773 tp->t_flags2 |= TF2_PLPMTU_MAXSEGSNT;
775 tp->t_flags2 &= ~TF2_PLPMTU_MAXSEGSNT;
778 * Before ESTABLISHED, force sending of initial options
779 * unless TCP set not to do any options.
780 * NOTE: we assume that the IP/TCP header plus TCP options
781 * always fit in a single mbuf, leaving room for a maximum
783 * max_linkhdr + sizeof (struct tcpiphdr) + optlen <= MCLBYTES
788 hdrlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
791 hdrlen = sizeof (struct tcpiphdr);
794 * Compute options for segment.
795 * We only have to care about SYN and established connection
796 * segments. Options for SYN-ACK segments are handled in TCP
800 if ((tp->t_flags & TF_NOOPT) == 0) {
801 /* Maximum segment size. */
802 if (flags & TH_SYN) {
803 tp->snd_nxt = tp->iss;
804 to.to_mss = tcp_mssopt(&tp->t_inpcb->inp_inc);
805 to.to_flags |= TOF_MSS;
808 * Only include the TFO option on the first
809 * transmission of the SYN|ACK on a
810 * passively-created TFO socket, as the presence of
811 * the TFO option may have caused the original
812 * SYN|ACK to have been dropped by a middlebox.
814 if (IS_FASTOPEN(tp->t_flags) &&
815 (tp->t_state == TCPS_SYN_RECEIVED) &&
816 (tp->t_rxtshift == 0)) {
817 to.to_tfo_len = TCP_FASTOPEN_COOKIE_LEN;
818 to.to_tfo_cookie = (u_char *)&tp->t_tfo_cookie;
819 to.to_flags |= TOF_FASTOPEN;
823 /* Window scaling. */
824 if ((flags & TH_SYN) && (tp->t_flags & TF_REQ_SCALE)) {
825 to.to_wscale = tp->request_r_scale;
826 to.to_flags |= TOF_SCALE;
829 if ((tp->t_flags & TF_RCVD_TSTMP) ||
830 ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) {
831 to.to_tsval = tcp_ts_getticks() + tp->ts_offset;
832 to.to_tsecr = tp->ts_recent;
833 to.to_flags |= TOF_TS;
834 /* Set receive buffer autosizing timestamp. */
835 if (tp->rfbuf_ts == 0 &&
836 (so->so_rcv.sb_flags & SB_AUTOSIZE))
837 tp->rfbuf_ts = tcp_ts_getticks();
839 /* Selective ACK's. */
840 if (tp->t_flags & TF_SACK_PERMIT) {
842 to.to_flags |= TOF_SACKPERM;
843 else if (TCPS_HAVEESTABLISHED(tp->t_state) &&
844 (tp->t_flags & TF_SACK_PERMIT) &&
845 tp->rcv_numsacks > 0) {
846 to.to_flags |= TOF_SACK;
847 to.to_nsacks = tp->rcv_numsacks;
848 to.to_sacks = (u_char *)tp->sackblks;
851 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
852 /* TCP-MD5 (RFC2385). */
854 * Check that TCP_MD5SIG is enabled in tcpcb to
855 * account the size needed to set this TCP option.
857 if (tp->t_flags & TF_SIGNATURE)
858 to.to_flags |= TOF_SIGNATURE;
859 #endif /* TCP_SIGNATURE */
861 /* Processing the options. */
862 hdrlen += optlen = tcp_addoptions(&to, opt);
866 * Adjust data length if insertion of options will
867 * bump the packet length beyond the t_maxseg length.
868 * Clear the FIN bit because we cut off the tail of
871 if (len + optlen + ipoptlen > tp->t_maxseg) {
876 u_int if_hw_tsomaxsegcount;
877 u_int if_hw_tsomaxsegsize;
882 /* extract TSO information */
883 if_hw_tsomax = tp->t_tsomax;
884 if_hw_tsomaxsegcount = tp->t_tsomaxsegcount;
885 if_hw_tsomaxsegsize = tp->t_tsomaxsegsize;
888 * Limit a TSO burst to prevent it from
889 * overflowing or exceeding the maximum length
890 * allowed by the network interface:
892 KASSERT(ipoptlen == 0,
893 ("%s: TSO can't do IP options", __func__));
896 * Check if we should limit by maximum payload
899 if (if_hw_tsomax != 0) {
900 /* compute maximum TSO length */
901 max_len = (if_hw_tsomax - hdrlen -
905 } else if (len > max_len) {
912 * Check if we should limit by maximum segment
915 if (if_hw_tsomaxsegcount != 0 &&
916 if_hw_tsomaxsegsize != 0) {
918 * Subtract one segment for the LINK
919 * and TCP/IP headers mbuf that will
920 * be prepended to this mbuf chain
921 * after the code in this section
922 * limits the number of mbufs in the
923 * chain to if_hw_tsomaxsegcount.
925 if_hw_tsomaxsegcount -= 1;
927 mb = sbsndmbuf(&so->so_snd, off, &moff);
929 while (mb != NULL && max_len < len) {
934 * Get length of mbuf fragment
935 * and how many hardware frags,
936 * rounded up, it would use:
938 mlen = (mb->m_len - moff);
939 frags = howmany(mlen,
940 if_hw_tsomaxsegsize);
942 /* Handle special case: Zero Length Mbuf */
947 * Check if the fragment limit
948 * will be reached or exceeded:
950 if (frags >= if_hw_tsomaxsegcount) {
952 if_hw_tsomaxsegcount *
953 if_hw_tsomaxsegsize);
957 if_hw_tsomaxsegcount -= frags;
963 } else if (len > max_len) {
970 * Prevent the last segment from being
971 * fractional unless the send sockbuf can be
974 max_len = (tp->t_maxseg - optlen);
975 if (((uint32_t)off + (uint32_t)len) <
976 sbavail(&so->so_snd)) {
977 moff = len % max_len;
985 * In case there are too many small fragments
988 if (len <= max_len) {
995 * Send the FIN in a separate segment
996 * after the bulk sending is done.
997 * We don't trust the TSO implementations
998 * to clear the FIN flag on all but the
1001 if (tp->t_flags & TF_NEEDFIN)
1005 len = tp->t_maxseg - optlen - ipoptlen;
1011 KASSERT(len + hdrlen + ipoptlen <= IP_MAXPACKET,
1012 ("%s: len > IP_MAXPACKET", __func__));
1014 /*#ifdef DIAGNOSTIC*/
1016 if (max_linkhdr + hdrlen > MCLBYTES)
1018 if (max_linkhdr + hdrlen > MHLEN)
1020 panic("tcphdr too big");
1024 * This KASSERT is here to catch edge cases at a well defined place.
1025 * Before, those had triggered (random) panic conditions further down.
1027 KASSERT(len >= 0, ("[%s:%d]: len < 0", __func__, __LINE__));
1030 * Grab a header mbuf, attaching a copy of data to
1031 * be transmitted, and initialize the header from
1032 * the template for sends on this connection.
1038 if ((tp->t_flags & TF_FORCEDATA) && len == 1)
1039 TCPSTAT_INC(tcps_sndprobe);
1040 else if (SEQ_LT(tp->snd_nxt, tp->snd_max) || sack_rxmit) {
1041 tp->t_sndrexmitpack++;
1042 TCPSTAT_INC(tcps_sndrexmitpack);
1043 TCPSTAT_ADD(tcps_sndrexmitbyte, len);
1045 TCPSTAT_INC(tcps_sndpack);
1046 TCPSTAT_ADD(tcps_sndbyte, len);
1049 if (MHLEN < hdrlen + max_linkhdr)
1050 m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
1053 m = m_gethdr(M_NOWAIT, MT_DATA);
1056 SOCKBUF_UNLOCK(&so->so_snd);
1062 m->m_data += max_linkhdr;
1066 * Start the m_copy functions from the closest mbuf
1067 * to the offset in the socket buffer chain.
1069 mb = sbsndptr(&so->so_snd, off, len, &moff);
1071 if (len <= MHLEN - hdrlen - max_linkhdr) {
1072 m_copydata(mb, moff, len,
1073 mtod(m, caddr_t) + hdrlen);
1076 m->m_next = m_copym(mb, moff, len, M_NOWAIT);
1077 if (m->m_next == NULL) {
1078 SOCKBUF_UNLOCK(&so->so_snd);
1087 * If we're sending everything we've got, set PUSH.
1088 * (This will keep happy those implementations which only
1089 * give data to the user when a buffer fills or
1092 if (((uint32_t)off + (uint32_t)len == sbused(&so->so_snd)) &&
1095 SOCKBUF_UNLOCK(&so->so_snd);
1097 SOCKBUF_UNLOCK(&so->so_snd);
1098 if (tp->t_flags & TF_ACKNOW)
1099 TCPSTAT_INC(tcps_sndacks);
1100 else if (flags & (TH_SYN|TH_FIN|TH_RST))
1101 TCPSTAT_INC(tcps_sndctrl);
1102 else if (SEQ_GT(tp->snd_up, tp->snd_una))
1103 TCPSTAT_INC(tcps_sndurg);
1105 TCPSTAT_INC(tcps_sndwinup);
1107 m = m_gethdr(M_NOWAIT, MT_DATA);
1114 if (isipv6 && (MHLEN < hdrlen + max_linkhdr) &&
1119 m->m_data += max_linkhdr;
1122 SOCKBUF_UNLOCK_ASSERT(&so->so_snd);
1123 m->m_pkthdr.rcvif = (struct ifnet *)0;
1125 mac_inpcb_create_mbuf(tp->t_inpcb, m);
1129 ip6 = mtod(m, struct ip6_hdr *);
1130 th = (struct tcphdr *)(ip6 + 1);
1131 tcpip_fillheaders(tp->t_inpcb, ip6, th);
1135 ip = mtod(m, struct ip *);
1136 ipov = (struct ipovly *)ip;
1137 th = (struct tcphdr *)(ip + 1);
1138 tcpip_fillheaders(tp->t_inpcb, ip, th);
1142 * Fill in fields, remembering maximum advertised
1143 * window for use in delaying messages about window sizes.
1144 * If resending a FIN, be sure not to use a new sequence number.
1146 if (flags & TH_FIN && tp->t_flags & TF_SENTFIN &&
1147 tp->snd_nxt == tp->snd_max)
1150 * If we are starting a connection, send ECN setup
1151 * SYN packet. If we are on a retransmit, we may
1152 * resend those bits a number of times as per
1155 if (tp->t_state == TCPS_SYN_SENT && V_tcp_do_ecn == 1) {
1156 if (tp->t_rxtshift >= 1) {
1157 if (tp->t_rxtshift <= V_tcp_ecn_maxretries)
1158 flags |= TH_ECE|TH_CWR;
1160 flags |= TH_ECE|TH_CWR;
1163 if (tp->t_state == TCPS_ESTABLISHED &&
1164 (tp->t_flags & TF_ECN_PERMIT)) {
1166 * If the peer has ECN, mark data packets with
1167 * ECN capable transmission (ECT).
1168 * Ignore pure ack packets, retransmissions and window probes.
1170 if (len > 0 && SEQ_GEQ(tp->snd_nxt, tp->snd_max) &&
1171 !((tp->t_flags & TF_FORCEDATA) && len == 1)) {
1174 ip6->ip6_flow |= htonl(IPTOS_ECN_ECT0 << 20);
1177 ip->ip_tos |= IPTOS_ECN_ECT0;
1178 TCPSTAT_INC(tcps_ecn_ect0);
1182 * Reply with proper ECN notifications.
1184 if (tp->t_flags & TF_ECN_SND_CWR) {
1186 tp->t_flags &= ~TF_ECN_SND_CWR;
1188 if (tp->t_flags & TF_ECN_SND_ECE)
1193 * If we are doing retransmissions, then snd_nxt will
1194 * not reflect the first unsent octet. For ACK only
1195 * packets, we do not want the sequence number of the
1196 * retransmitted packet, we want the sequence number
1197 * of the next unsent octet. So, if there is no data
1198 * (and no SYN or FIN), use snd_max instead of snd_nxt
1199 * when filling in ti_seq. But if we are in persist
1200 * state, snd_max might reflect one byte beyond the
1201 * right edge of the window, so use snd_nxt in that
1202 * case, since we know we aren't doing a retransmission.
1203 * (retransmit and persist are mutually exclusive...)
1205 if (sack_rxmit == 0) {
1206 if (len || (flags & (TH_SYN|TH_FIN)) ||
1207 tcp_timer_active(tp, TT_PERSIST))
1208 th->th_seq = htonl(tp->snd_nxt);
1210 th->th_seq = htonl(tp->snd_max);
1212 th->th_seq = htonl(p->rxmit);
1214 tp->sackhint.sack_bytes_rexmit += len;
1216 th->th_ack = htonl(tp->rcv_nxt);
1218 bcopy(opt, th + 1, optlen);
1219 th->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
1221 th->th_flags = flags;
1223 * Calculate receive window. Don't shrink window,
1224 * but avoid silly window syndrome.
1226 if (recwin < (so->so_rcv.sb_hiwat / 4) &&
1227 recwin < tp->t_maxseg)
1229 if (SEQ_GT(tp->rcv_adv, tp->rcv_nxt) &&
1230 recwin < (tp->rcv_adv - tp->rcv_nxt))
1231 recwin = (tp->rcv_adv - tp->rcv_nxt);
1234 * According to RFC1323 the window field in a SYN (i.e., a <SYN>
1235 * or <SYN,ACK>) segment itself is never scaled. The <SYN,ACK>
1236 * case is handled in syncache.
1239 th->th_win = htons((u_short)
1240 (min(sbspace(&so->so_rcv), TCP_MAXWIN)));
1242 th->th_win = htons((u_short)(recwin >> tp->rcv_scale));
1245 * Adjust the RXWIN0SENT flag - indicate that we have advertised
1246 * a 0 window. This may cause the remote transmitter to stall. This
1247 * flag tells soreceive() to disable delayed acknowledgements when
1248 * draining the buffer. This can occur if the receiver is attempting
1249 * to read more data than can be buffered prior to transmitting on
1252 if (th->th_win == 0) {
1254 tp->t_flags |= TF_RXWIN0SENT;
1256 tp->t_flags &= ~TF_RXWIN0SENT;
1257 if (SEQ_GT(tp->snd_up, tp->snd_nxt)) {
1258 th->th_urp = htons((u_short)(tp->snd_up - tp->snd_nxt));
1259 th->th_flags |= TH_URG;
1262 * If no urgent pointer to send, then we pull
1263 * the urgent pointer to the left edge of the send window
1264 * so that it doesn't drift into the send window on sequence
1265 * number wraparound.
1267 tp->snd_up = tp->snd_una; /* drag it along */
1270 * Put TCP length in extended header, and then
1271 * checksum extended header and data.
1273 m->m_pkthdr.len = hdrlen + len; /* in6_cksum() need this */
1274 m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
1276 #if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
1277 if (to.to_flags & TOF_SIGNATURE) {
1279 * Calculate MD5 signature and put it into the place
1280 * determined before.
1281 * NOTE: since TCP options buffer doesn't point into
1282 * mbuf's data, calculate offset and use it.
1284 if (!TCPMD5_ENABLED() || TCPMD5_OUTPUT(m, th,
1285 (u_char *)(th + 1) + (to.to_signature - opt)) != 0) {
1287 * Do not send segment if the calculation of MD5
1288 * digest has failed.
1297 * There is no need to fill in ip6_plen right now.
1298 * It will be filled later by ip6_output.
1300 m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
1301 th->th_sum = in6_cksum_pseudo(ip6, sizeof(struct tcphdr) +
1302 optlen + len, IPPROTO_TCP, 0);
1305 #if defined(INET6) && defined(INET)
1310 m->m_pkthdr.csum_flags = CSUM_TCP;
1311 th->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
1312 htons(sizeof(struct tcphdr) + IPPROTO_TCP + len + optlen));
1314 /* IP version must be set here for ipv4/ipv6 checking later */
1315 KASSERT(ip->ip_v == IPVERSION,
1316 ("%s: IP version incorrect: %d", __func__, ip->ip_v));
1321 * Enable TSO and specify the size of the segments.
1322 * The TCP pseudo header checksum is always provided.
1325 KASSERT(len > tp->t_maxseg - optlen,
1326 ("%s: len <= tso_segsz", __func__));
1327 m->m_pkthdr.csum_flags |= CSUM_TSO;
1328 m->m_pkthdr.tso_segsz = tp->t_maxseg - optlen;
1331 #if defined(IPSEC) || defined(IPSEC_SUPPORT)
1332 KASSERT(len + hdrlen + ipoptlen - ipsec_optlen == m_length(m, NULL),
1333 ("%s: mbuf chain shorter than expected: %d + %u + %u - %u != %u",
1334 __func__, len, hdrlen, ipoptlen, ipsec_optlen, m_length(m, NULL)));
1336 KASSERT(len + hdrlen + ipoptlen == m_length(m, NULL),
1337 ("%s: mbuf chain shorter than expected: %d + %u + %u != %u",
1338 __func__, len, hdrlen, ipoptlen, m_length(m, NULL)));
1342 /* Run HHOOK_TCP_ESTABLISHED_OUT helper hooks. */
1343 hhook_run_tcp_est_out(tp, th, &to, len, tso);
1350 if (so->so_options & SO_DEBUG) {
1356 save = ipov->ih_len;
1357 ipov->ih_len = htons(m->m_pkthdr.len /* - hdrlen + (th->th_off << 2) */);
1359 tcp_trace(TA_OUTPUT, tp->t_state, tp, mtod(m, void *), th, 0);
1363 ipov->ih_len = save;
1365 #endif /* TCPDEBUG */
1366 TCP_PROBE3(debug__output, tp, th, m);
1369 * Fill in IP length and desired time to live and
1370 * send to IP level. There should be a better way
1371 * to handle ttl and tos; we could keep them in
1372 * the template, but need a way to checksum without them.
1375 * m->m_pkthdr.len should have been set before checksum calculation,
1376 * because in6_cksum() need it.
1380 struct route_in6 ro;
1382 bzero(&ro, sizeof(ro));
1384 * we separately set hoplimit for every segment, since the
1385 * user might want to change the value via setsockopt.
1386 * Also, desired default hop limit might be changed via
1387 * Neighbor Discovery.
1389 ip6->ip6_hlim = in6_selecthlim(tp->t_inpcb, NULL);
1392 * Set the packet size here for the benefit of DTrace probes.
1393 * ip6_output() will set it properly; it's supposed to include
1394 * the option header lengths as well.
1396 ip6->ip6_plen = htons(m->m_pkthdr.len - sizeof(*ip6));
1398 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss)
1399 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1401 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1403 if (tp->t_state == TCPS_SYN_SENT)
1404 TCP_PROBE5(connect__request, NULL, tp, ip6, tp, th);
1406 TCP_PROBE5(send, NULL, tp, ip6, tp, th);
1409 /* Save packet, if requested. */
1410 tcp_pcap_add(th, m, &(tp->t_outpkts));
1413 /* TODO: IPv6 IP6TOS_ECT bit on */
1414 error = ip6_output(m, tp->t_inpcb->in6p_outputopts, &ro,
1415 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0),
1416 NULL, NULL, tp->t_inpcb);
1418 if (error == EMSGSIZE && ro.ro_rt != NULL)
1419 mtu = ro.ro_rt->rt_mtu;
1423 #if defined(INET) && defined(INET6)
1428 ip->ip_len = htons(m->m_pkthdr.len);
1430 if (tp->t_inpcb->inp_vflag & INP_IPV6PROTO)
1431 ip->ip_ttl = in6_selecthlim(tp->t_inpcb, NULL);
1434 * If we do path MTU discovery, then we set DF on every packet.
1435 * This might not be the best thing to do according to RFC3390
1436 * Section 2. However the tcp hostcache migitates the problem
1437 * so it affects only the first tcp connection with a host.
1439 * NB: Don't set DF on small MTU/MSS to have a safe fallback.
1441 if (V_path_mtu_discovery && tp->t_maxseg > V_tcp_minmss) {
1442 ip->ip_off |= htons(IP_DF);
1443 tp->t_flags2 |= TF2_PLPMTU_PMTUD;
1445 tp->t_flags2 &= ~TF2_PLPMTU_PMTUD;
1448 if (tp->t_state == TCPS_SYN_SENT)
1449 TCP_PROBE5(connect__request, NULL, tp, ip, tp, th);
1451 TCP_PROBE5(send, NULL, tp, ip, tp, th);
1454 /* Save packet, if requested. */
1455 tcp_pcap_add(th, m, &(tp->t_outpkts));
1458 error = ip_output(m, tp->t_inpcb->inp_options, &tp->t_inpcb->inp_route,
1459 ((so->so_options & SO_DONTROUTE) ? IP_ROUTETOIF : 0), 0,
1462 if (error == EMSGSIZE && tp->t_inpcb->inp_route.ro_rt != NULL)
1463 mtu = tp->t_inpcb->inp_route.ro_rt->rt_mtu;
1469 * In transmit state, time the transmission and arrange for
1470 * the retransmit. In persist state, just set snd_max.
1472 if ((tp->t_flags & TF_FORCEDATA) == 0 ||
1473 !tcp_timer_active(tp, TT_PERSIST)) {
1474 tcp_seq startseq = tp->snd_nxt;
1477 * Advance snd_nxt over sequence space of this segment.
1479 if (flags & (TH_SYN|TH_FIN)) {
1482 if (flags & TH_FIN) {
1484 tp->t_flags |= TF_SENTFIN;
1490 if (SEQ_GT(tp->snd_nxt, tp->snd_max)) {
1491 tp->snd_max = tp->snd_nxt;
1493 * Time this transmission if not a retransmission and
1494 * not currently timing anything.
1496 if (tp->t_rtttime == 0) {
1497 tp->t_rtttime = ticks;
1498 tp->t_rtseq = startseq;
1499 TCPSTAT_INC(tcps_segstimed);
1504 * Set retransmit timer if not currently set,
1505 * and not doing a pure ack or a keep-alive probe.
1506 * Initial value for retransmit timer is smoothed
1507 * round-trip time + 2 * round-trip time variance.
1508 * Initialize shift counter which is used for backoff
1509 * of retransmit time.
1512 if (!tcp_timer_active(tp, TT_REXMT) &&
1513 ((sack_rxmit && tp->snd_nxt != tp->snd_max) ||
1514 (tp->snd_nxt != tp->snd_una))) {
1515 if (tcp_timer_active(tp, TT_PERSIST)) {
1516 tcp_timer_activate(tp, TT_PERSIST, 0);
1519 tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
1520 } else if (len == 0 && sbavail(&so->so_snd) &&
1521 !tcp_timer_active(tp, TT_REXMT) &&
1522 !tcp_timer_active(tp, TT_PERSIST)) {
1524 * Avoid a situation where we do not set persist timer
1525 * after a zero window condition. For example:
1526 * 1) A -> B: packet with enough data to fill the window
1527 * 2) B -> A: ACK for #1 + new data (0 window
1529 * 3) A -> B: ACK for #2, 0 len packet
1531 * In this case, A will not activate the persist timer,
1532 * because it chose to send a packet. Unless tcp_output
1533 * is called for some other reason (delayed ack timer,
1534 * another input packet from B, socket syscall), A will
1535 * not send zero window probes.
1537 * So, if you send a 0-length packet, but there is data
1538 * in the socket buffer, and neither the rexmt or
1539 * persist timer is already set, then activate the
1547 * Persist case, update snd_max but since we are in
1548 * persist mode (no window) we do not update snd_nxt.
1553 if (flags & TH_FIN) {
1555 tp->t_flags |= TF_SENTFIN;
1557 if (SEQ_GT(tp->snd_nxt + xlen, tp->snd_max))
1558 tp->snd_max = tp->snd_nxt + xlen;
1564 * We know that the packet was lost, so back out the
1565 * sequence number advance, if any.
1567 * If the error is EPERM the packet got blocked by the
1568 * local firewall. Normally we should terminate the
1569 * connection but the blocking may have been spurious
1570 * due to a firewall reconfiguration cycle. So we treat
1571 * it like a packet loss and let the retransmit timer and
1572 * timeouts do their work over time.
1573 * XXX: It is a POLA question whether calling tcp_drop right
1574 * away would be the really correct behavior instead.
1576 if (((tp->t_flags & TF_FORCEDATA) == 0 ||
1577 !tcp_timer_active(tp, TT_PERSIST)) &&
1578 ((flags & TH_SYN) == 0) &&
1582 tp->sackhint.sack_bytes_rexmit -= len;
1583 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
1584 ("sackhint bytes rtx >= 0"));
1588 SOCKBUF_UNLOCK_ASSERT(&so->so_snd); /* Check gotos. */
1591 tp->t_softerror = error;
1594 tp->t_softerror = error;
1597 TCP_XMIT_TIMER_ASSERT(tp, len, flags);
1598 tp->snd_cwnd = tp->t_maxseg;
1602 * For some reason the interface we used initially
1603 * to send segments changed to another or lowered
1605 * If TSO was active we either got an interface
1606 * without TSO capabilits or TSO was turned off.
1607 * If we obtained mtu from ip_output() then update
1611 tp->t_flags &= ~TF_TSO;
1613 tcp_mss_update(tp, -1, mtu, NULL, NULL);
1621 if (TCPS_HAVERCVDSYN(tp->t_state)) {
1622 tp->t_softerror = error;
1630 TCPSTAT_INC(tcps_sndtotal);
1633 * Data sent (as far as we can tell).
1634 * If this advertises a larger window than any other segment,
1635 * then remember the size of the advertised window.
1636 * Any pending ACK has now been sent.
1638 if (SEQ_GT(tp->rcv_nxt + recwin, tp->rcv_adv))
1639 tp->rcv_adv = tp->rcv_nxt + recwin;
1640 tp->last_ack_sent = tp->rcv_nxt;
1641 tp->t_flags &= ~(TF_ACKNOW | TF_DELACK);
1642 if (tcp_timer_active(tp, TT_DELACK))
1643 tcp_timer_activate(tp, TT_DELACK, 0);
1646 * This completely breaks TCP if newreno is turned on. What happens
1647 * is that if delayed-acks are turned on on the receiver, this code
1648 * on the transmitter effectively destroys the TCP window, forcing
1649 * it to four packets (1.5Kx4 = 6K window).
1651 if (sendalot && --maxburst)
1660 tcp_setpersist(struct tcpcb *tp)
1662 int t = ((tp->t_srtt >> 2) + tp->t_rttvar) >> 1;
1665 tp->t_flags &= ~TF_PREVVALID;
1666 if (tcp_timer_active(tp, TT_REXMT))
1667 panic("tcp_setpersist: retransmit pending");
1669 * Start/restart persistence timer.
1671 TCPT_RANGESET(tt, t * tcp_backoff[tp->t_rxtshift],
1672 tcp_persmin, tcp_persmax);
1673 tcp_timer_activate(tp, TT_PERSIST, tt);
1674 if (tp->t_rxtshift < TCP_MAXRXTSHIFT)
1679 * Insert TCP options according to the supplied parameters to the place
1680 * optp in a consistent way. Can handle unaligned destinations.
1682 * The order of the option processing is crucial for optimal packing and
1683 * alignment for the scarce option space.
1685 * The optimal order for a SYN/SYN-ACK segment is:
1686 * MSS (4) + NOP (1) + Window scale (3) + SACK permitted (2) +
1687 * Timestamp (10) + Signature (18) = 38 bytes out of a maximum of 40.
1689 * The SACK options should be last. SACK blocks consume 8*n+2 bytes.
1690 * So a full size SACK blocks option is 34 bytes (with 4 SACK blocks).
1691 * At minimum we need 10 bytes (to generate 1 SACK block). If both
1692 * TCP Timestamps (12 bytes) and TCP Signatures (18 bytes) are present,
1693 * we only have 10 bytes for SACK options (40 - (12 + 18)).
1696 tcp_addoptions(struct tcpopt *to, u_char *optp)
1698 u_int32_t mask, optlen = 0;
1700 for (mask = 1; mask < TOF_MAXOPT; mask <<= 1) {
1701 if ((to->to_flags & mask) != mask)
1703 if (optlen == TCP_MAXOLEN)
1705 switch (to->to_flags & mask) {
1707 while (optlen % 4) {
1708 optlen += TCPOLEN_NOP;
1709 *optp++ = TCPOPT_NOP;
1711 if (TCP_MAXOLEN - optlen < TCPOLEN_MAXSEG)
1713 optlen += TCPOLEN_MAXSEG;
1714 *optp++ = TCPOPT_MAXSEG;
1715 *optp++ = TCPOLEN_MAXSEG;
1716 to->to_mss = htons(to->to_mss);
1717 bcopy((u_char *)&to->to_mss, optp, sizeof(to->to_mss));
1718 optp += sizeof(to->to_mss);
1721 while (!optlen || optlen % 2 != 1) {
1722 optlen += TCPOLEN_NOP;
1723 *optp++ = TCPOPT_NOP;
1725 if (TCP_MAXOLEN - optlen < TCPOLEN_WINDOW)
1727 optlen += TCPOLEN_WINDOW;
1728 *optp++ = TCPOPT_WINDOW;
1729 *optp++ = TCPOLEN_WINDOW;
1730 *optp++ = to->to_wscale;
1733 while (optlen % 2) {
1734 optlen += TCPOLEN_NOP;
1735 *optp++ = TCPOPT_NOP;
1737 if (TCP_MAXOLEN - optlen < TCPOLEN_SACK_PERMITTED)
1739 optlen += TCPOLEN_SACK_PERMITTED;
1740 *optp++ = TCPOPT_SACK_PERMITTED;
1741 *optp++ = TCPOLEN_SACK_PERMITTED;
1744 while (!optlen || optlen % 4 != 2) {
1745 optlen += TCPOLEN_NOP;
1746 *optp++ = TCPOPT_NOP;
1748 if (TCP_MAXOLEN - optlen < TCPOLEN_TIMESTAMP)
1750 optlen += TCPOLEN_TIMESTAMP;
1751 *optp++ = TCPOPT_TIMESTAMP;
1752 *optp++ = TCPOLEN_TIMESTAMP;
1753 to->to_tsval = htonl(to->to_tsval);
1754 to->to_tsecr = htonl(to->to_tsecr);
1755 bcopy((u_char *)&to->to_tsval, optp, sizeof(to->to_tsval));
1756 optp += sizeof(to->to_tsval);
1757 bcopy((u_char *)&to->to_tsecr, optp, sizeof(to->to_tsecr));
1758 optp += sizeof(to->to_tsecr);
1762 int siglen = TCPOLEN_SIGNATURE - 2;
1764 while (!optlen || optlen % 4 != 2) {
1765 optlen += TCPOLEN_NOP;
1766 *optp++ = TCPOPT_NOP;
1768 if (TCP_MAXOLEN - optlen < TCPOLEN_SIGNATURE) {
1769 to->to_flags &= ~TOF_SIGNATURE;
1772 optlen += TCPOLEN_SIGNATURE;
1773 *optp++ = TCPOPT_SIGNATURE;
1774 *optp++ = TCPOLEN_SIGNATURE;
1775 to->to_signature = optp;
1783 struct sackblk *sack = (struct sackblk *)to->to_sacks;
1786 while (!optlen || optlen % 4 != 2) {
1787 optlen += TCPOLEN_NOP;
1788 *optp++ = TCPOPT_NOP;
1790 if (TCP_MAXOLEN - optlen < TCPOLEN_SACKHDR + TCPOLEN_SACK)
1792 optlen += TCPOLEN_SACKHDR;
1793 *optp++ = TCPOPT_SACK;
1794 sackblks = min(to->to_nsacks,
1795 (TCP_MAXOLEN - optlen) / TCPOLEN_SACK);
1796 *optp++ = TCPOLEN_SACKHDR + sackblks * TCPOLEN_SACK;
1797 while (sackblks--) {
1798 sack_seq = htonl(sack->start);
1799 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1800 optp += sizeof(sack_seq);
1801 sack_seq = htonl(sack->end);
1802 bcopy((u_char *)&sack_seq, optp, sizeof(sack_seq));
1803 optp += sizeof(sack_seq);
1804 optlen += TCPOLEN_SACK;
1807 TCPSTAT_INC(tcps_sack_send_blocks);
1815 /* XXX is there any point to aligning this option? */
1816 total_len = TCPOLEN_FAST_OPEN_EMPTY + to->to_tfo_len;
1817 if (TCP_MAXOLEN - optlen < total_len)
1819 *optp++ = TCPOPT_FAST_OPEN;
1820 *optp++ = total_len;
1821 if (to->to_tfo_len > 0) {
1822 bcopy(to->to_tfo_cookie, optp, to->to_tfo_len);
1823 optp += to->to_tfo_len;
1825 optlen += total_len;
1830 panic("%s: unknown TCP option type", __func__);
1835 /* Terminate and pad TCP options to a 4 byte boundary. */
1837 optlen += TCPOLEN_EOL;
1838 *optp++ = TCPOPT_EOL;
1841 * According to RFC 793 (STD0007):
1842 * "The content of the header beyond the End-of-Option option
1843 * must be header padding (i.e., zero)."
1844 * and later: "The padding is composed of zeros."
1846 while (optlen % 4) {
1847 optlen += TCPOLEN_PAD;
1848 *optp++ = TCPOPT_PAD;
1851 KASSERT(optlen <= TCP_MAXOLEN, ("%s: TCP options too long", __func__));